MC9S08GB60A Datasheet, PDF (81/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 6
Parallel Input/Output
6.1 Introduction
This section explains software controls related to parallel input/output (I/O). The MC9S08GBxxA has
seven I/O ports which include a total of 56 general-purpose I/O pins (one of these pins is output only). The
MC9S08GTxxA has six I/O ports which include a total of up to 39 general-purpose I/O pins (one pin,
PTG0, is output only). See Chapter 2, “Pins and Connections,” for more information about the logic and
hardware aspects of these pins.
Many of these pins are shared with on-chip peripherals such as timer systems, external interrupts, or
keyboard interrupts. When these other modules are not controlling the port pins, they revert to
general-purpose I/O control. For each I/O pin, a port data bit provides access to input (read) and output
(write) data, a data direction bit controls the direction of the pin, and a pullup enable bit enables an internal
pullup device (provided the pin is configured as an input), and a slew rate control bit controls the rise and
fall times of the pins.
NOTE
Not all general-purpose I/O pins are available on all packages. To avoid
extra current drain from floating input pins, the user’s reset initialization
routine in the application program should either enable on-chip pullup
devices or change the direction of unconnected pins to outputs so the pins
do not float.
MC9S08GB60A Data Sheet, Rev. 2
Freescale Semiconductor
81